1. Field of the Invention
The present invention relates to antenna devices preferably for use in near field communication (NFC) systems and so forth and to communication appliances equipped with such an antenna device.
2. Description of the Related Art
It is becoming increasingly common for NFC systems to be incorporated into small-sized electronic appliances such as cellular phone terminals and tablet PCs. In particular, in the case of a cellular phone terminal, an NFC antenna is demanded with which communication can be performed in a state where a display surface of the cellular phone terminal is made to face an antenna device of a communication partner.
However, as the bodies of cellular phone terminals become smaller and the degree of integration of cellular phone terminals becomes ever higher, it is becoming increasingly difficult to secure a space in which to mount an antenna device in cellular phone terminals. Furthermore, there is also a tendency for display devices (displays) to becomes thinner while the display area thereof becomes larger, and it is often the case that a metal plate (conductor layer) that doubles as a shield is arranged over the entirety of a non-display surface of a display panel in order to reduce damage caused by external impacts. In such a case, there is a problem in that the antenna characteristics are degraded by unwanted coupling between the antenna device and the metal plate when the antenna device is arranged close to the display device.
However, Japanese Unexamined Patent Application Publication No. 2006-195802 discloses an apparatus in which an antenna is formed of a transparent electrode such as an ITO electrode on the display device and consequently a display surface of the display device can be used as a communication surface.
The conductivity of a transparent electrode such as an ITO electrode is very low compared with that of copper or aluminum. Consequently, conductor loss is large and excellent antenna characteristics cannot be obtained when an antenna is formed of a transparent electrode such as an ITO electrode as described in Japanese Unexamined Patent Application Publication No. 2006-195802.